Operating mechanism for a parking brake

ABSTRACT

An operating mechanism  1  for operating a parking brake, particularly for motor vehicles, includes a motor unit  10, 20  and an eccentric assembly  30, 40 , for transforming the rotational motion of the motor unit  10, 20  into a linear motion, by using the eccentric principle, wherein at least one braking cable  70  is tightened or released for an operation of at least one parking brake.

CROSS-REFERENCE TO RELATED APPLICATION

This is the U.S. National Phase of International Application No.PCT/EP03/03055 filed 24 Mar. 2003, the entire disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an operating mechanism for operating aparking brake, particularly a parking brake for a motor vehicle wherethe brake is driven by an electric motor.

PRIOR ART

The prior art provides different solutions for parking brakes andhandbrakes. Parking brakes for motor vehicles in general act on the backtires of the vehicle and are activated via a sheathed cable. The brakecan either be operated by a hand lever or a foot pedal. Since theoperating of the parking brake typically requires substantial effort, itis not operated as required by particularly elderly drivers. Therefore,on the one hand a safety risk occurs, since the vehicle could roll awaywhile parking and on the other hand the use of the parking brake isuncomfortable. To reduce this effort and to provide a comfortableoperation of the parking brake, parking brakes are known in the priorart, which are for example driven by an electric motor instead ofmanually.

DE 198 18 339 C1 discloses a braking system in which the brakes areoperated by a cable roll, driven by an electric motor. The ends of thebraking cable assemblies of the back tires are therefore connected tothe opposing sides of the circumference of the cable roll. Duringrotation of the cable roll, equal distances of both braking cables aresimultaneously rolled up to the cable roll and thereby the back tiresare uniformly braked. It is overly costly to adjust the length of thebraking cables to obtain a uniform operation of the brakes. In addition,the braking cables must regularly be checked and adjusted, as they maybecome misadjusted during use.

A further electric parking brake system for passenger cars is describedin WO 98/56633. The document discloses a parking brake operatingmechanism for passenger cars with an actuating mechanism comprising amotor-powered drive, for example an electric motor, for tightening orreleasing of a braking cable of a vehicle's braking system. Theoperating mechanism comprises an actuator for the braking cable,adjustable by the drive, which is related to a force measuringmechanism.

DE 197 55 933 discloses an operating mechanism for parking brakes formotor vehicles, in which an actuator comprises a motor-powered drive fortightening or releasing of braking cable assemblies of a braking systemof a vehicle. The drive is in connection with an element that isrotatable around its longitudinal axis and not displaceable with respectto the longitudinal axis. The element is coupled with a telescopicassembly that is displaceably arranged in the direction of thelongitudinal axis, wherein the axial length of the telescopic assemblyis increased or decreased dependent on the rotational direction of theelement. Each of the axial ends of the telescopic assembly is directlyor indirectly connected to one braking cable for one brake of thebraking system, respectively.

Finally, DE 100 43 739.7 discloses a parking brake for motor vehicleshaving at least two braking cable assemblies, the parking brakecomprising an actuator with couple elements, wherein two braking cableassemblies are coupled to the couple elements at two couple locations.Further an operating mechanism is provided, arranged, and connected withthe actuator in such a way that the distance of the couple locations canbe changed in a controlled manner, whereby a relative movement of thecouple locations to or away from each other is enabled.

This construction disadvantageously consists of a plurality ofexpensively producible components, and requires regular maintenance.Therefore, this prior art operating mechanism is comparatively less costeffective in manufacturing and maintenance and space consuming becauseof the complex construction.

It is therefore the technical problem underlying the present invention,to provide an operating mechanism for a parking brake that can easily bemanufactured and that guaranties a safe and malfunction free operation.

SUMMARY OF THE DISCLOSURE

The present disclosure solves the above problem by an operatingmechanism for operating at least one parking brake, particularly formotor vehicles. The operating mechanism is connected with the brakes viabraking cable assemblies and replaces the manual lever brake or footpedal. By using the operating mechanism, the brake cables within thebraking cable assemblies are tightened or released by a motor force.

The operating mechanism comprises a motor unit for driving the operatingmechanism and an eccentric assembly that transforms the rotationalmotion of the motor unit into a linear motion by using the eccentricprinciple, wherein at least one braking cable is tightened or releasedfor operating the at least one parking brake. The eccentric assemblyuses the eccentric principle, whereby rotational motions are transformedinto linear motions by means of a crank gear or a cam gear.

In a first preferred embodiment according to the disclosure, theeccentric assembly comprises a cam connected to the motor unit and atappet displaceable by the cam.

The parking brake according to the disclosure thus comprises just a fewcomponents and is very robust and low maintenance. In addition theoperating mechanism can be built very compact and therefore occupieslittle space in or at the vehicle. In a first embodiment, the forcecompensation between both connected brakes is done directly via thebraking cable, which is deviated within the operating mechanism, butremains axially displaceable. Tensile forces acting on the ends of thebraking cables are compensated. Therefore, the same force acts in eachbraking cable half and the brakes actuated thereby have the same brakingeffect.

In a further preferred embodiment, the tappet is arranged between twoguide rolls. The at least one braking cable runs via the guide rolls andthe tappet with low friction. If no guide rolls are provided, thebraking cable is guided over sliding faces. Therefore a lubrication ofthe sliding faces is needed.

In a further preferred embodiment, the tappet is curved at the cableguiding side to direct the braking cable along the desired path and toreduce the friction between tappet and braking cable. Therefore, thebraking cable is rotatably supported at, rather than simply slidingover, the guiding components within the operating mechanism. Thisfacilitates the force compensation between both braking cable halves andincreases the lifetime of the braking cable.

According to a further preferred embodiment of the eccentric assemblyaccording to the disclosure, the tappet is connected to a first and asecond cable holder, displaceable in the direction of the brakingcables, wherein by a displacement of the tappet causes a displacement ofthe first and the second cable holders, for tightening or releasing ofrespectively one braking cable half, connected to one of the cableholders. The cable holders are connected by means of a flexibleconnecting element that runs via the tappet. The braking cable isdivided in this embodiment. The first cable holder is connected with afirst braking cable half and the second cable holder with a secondbraking cable half, to operate respectively at least one brake. Theconnecting element can slide on the cable guiding end of the tappet and,thus, provides the necessary force compensation between the two brakingcable halves. One advantage of this embodiment is that both brakingcable halves are guided substantially straight and are not deviated. Thedeviated connecting element can be configured stronger compared to thebraking cable halves, corresponding to the higher load.

In a further embodiment of the present disclosure the tappet comprises aguide roll on the side of the connecting element for guiding theconnecting element and for decreasing the friction between tappet andthe connecting element. The connecting element therefore is rotatablyguided by the guide roll and not slidingly onto the tappet, whichreduces the friction at the connecting element.

In a further preferred embodiment of the disclosure the cam is shaped sothat it comprises an assembly position, with minimal displacement of thetappet, and a working range, in which the at least one braking cable istightened or released. When the cam is situated in its assemblyposition, the braking cable is in its most released condition andtherefore it can be easily assembled to the brake.

In a further preferred embodiment, a force measuring device is providedwithin the operating mechanism to determine the braking force generatedby the operating mechanism, wherein said force measuring device isintegrated in the braking cable, integrated in the tappet, or connectedto one guide roll. The motor unit of the operating mechanism iscontrolled by an electronic controller, which receives and interpretssignals of the force measuring device. Thereby it is guarantied, thatduring the automatic tightening of the parking brake a sufficient brakeeffect is achieved. Further an overload of the operating mechanism aswell as the connected braking cables and brakes is prevented.

In a further preferred embodiment, the motor unit comprises a motor anda gearbox connected thereto. Further, according to the disclosure, themotor is provided as an electric motor and the gearbox is provided as aplanetary gear.

Finally, the operating mechanism comprises a housing.

Further preferred embodiments of the disclosure arise from the dependentclaims.

SHORT DESCRIPTION OF THE DRAWINGS

In the following the preferred embodiments of the present disclosure aredescribed with reference to the drawings, in which:

FIG. 1 is a perspective view of an operating mechanism according to thedisclosure with an open housing;

FIG. 2 is a perspective view of an operating mechanism according to thedisclosure without a housing;

FIG. 3 is a top plan view of an operating mechanism according to thedisclosure with an open housing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present disclosure provides an operating mechanism for a parkingbrake that is based on the use of the eccentric principle for tighteningor releasing of at least one braking cable for operating at least oneparking brake. The eccentric principle describes the transformation ofrotational into translational motions by the use of crank or cam gears.

In a crank gear, the eccentric principle is achieved by positioning acircular disc on a rotatable shaft such that the circular disc isnon-centric or offset, wherein a connecting rod transmits movement ofthe disc to an element to be linearly moved. A crank gear in acombustion engine is one example of a device that uses the eccentricprinciple to convert rotational movement to linear movement. In a camgear, the conversion of rotational movement into a linearly translatingmovement is achieved by actuating a linear guided tappet by means of acam, which is non-symmetric about its rotational axis. This is used, forexample, to control the valves of a combustion engine.

FIG. 1 illustrates one embodiment of the operating mechanism accordingto the disclosure. In this embodiment, the operating mechanism 1 of theparking brake comprises a motor unit 10, 20 and an eccentric assembly30, 40, that adjusts, such as by tightening or releasing, at least onebraking cable. The eccentric mechanism 30, 40 may be provided as a camgear. A cam 30 is connected to the output shaft 25 of the motor unit 10,20. The cam 30 moves a slidably mounted tappet 40 which, on a sideopposite the cam 30, actuates a braking cable 70. Thereby, the brakingcable 70, which is connected to at least one brake, is tightened orreleased. In this manner, the braking cable 70 may transmit brakingforces via two braking cable assemblies (not shown) to the connectedbrakes. The braking cable 70 is tightened or released by the actuationof the tappet 40 for a uniform operation of the connected brakes. Theuniform operation of the connected brakes is achieved, in such a way,that the braking cable within the operating mechanism is in facttightened and released, but still is displaceably guided via slidingfaces and tappet 40. Different operating forces of the connected brakescan compensate themselves directly via the braking cable.

Preferably according to the invention, the operating mechanism 1 isdriven by a motor unit 10, 20. The motor unit 10, 20 is comprised of anydesired motor-gearbox-combination or just of a motor. If providedwithout a gearbox, a step motor, for example, may be used as motor, inwhich electrical impulses are transformed into a defined angle positionof its rotor. Alternatively, the motor unit 10, 20 may consist of amotor 10 with a connected gearbox 20. The rotational motion generated bythe motor 10 is transformed by the gearbox 20 to decrease the number ofrevolutions of the motor shaft, thereby increasing torque.

The motor 10 is preferably provided as an electric motor. Alternatively,the motor 10 may be provided as a hydraulic motor or as a pressured airdriven motor. In the illustrated embodiment, the motor 10 directlydrives the gearbox 20. Alternative arrangements of the motor 10 andgearbox 20 are conceivable. The gear box 20 may be provided as anenclosed planetary gear. Therefore, it is substantially maintenance freeand malfunction resistant. Additionally, the planetary gear has acompact configuration, so that the complete operating mechanism can beprovided in a compact assembly. As noted above, the gearbox 20 may beprovided as a reduction gearbox, wherein the selected reduction of thegear box 20 is adapted to the motor 10. The reduction of the gearbox 20is preferably chosen so that the motor 10 works in a torque-optimalrange. Further, fast operating times can be achieved by an appropriateselection of the reduction of gearbox 20.

The cam 30 is axially mounted to the output shaft 25 of the gear box 20.A positive connection may be provided between the cam 30 and the outputshaft 25 of the gear box 20, to transmit high torques. Frictionallyengaged connections, such as a shrinking connection, may be used toprovide the positive connection. High-strength plastic materials ormetals are preferably used as material for the cam 30. In the preferredembodiment, the cam 30 is made of steel. The shape of the cam 30 definesthe actuation of the tappet 40 and therefore the tightening andreleasing of the braking cable 70. In that way, different tensile forcescan be transmitted to the braking cable 70 by different gradients of thecam 30. To this end, the cam 30 can be shaped arbitrarily. In thepreferred embodiment, the cam 30 is approximately elliptically shaped.In this embodiment, the difference between the largest and the smallestradii of the elliptical profile of the cam 30 corresponds to the maximumtranslational displacement of the tappet 40.

The cam 30 is shaped so that it comprises an assembly position and anoperating range. The assembly position of the cam 30 is qualified insuch a way, that the tappet 40 is minimally or not displaced. Therefore,the braking cable 70 is loaded minimally or not at all, whereby thebraking cable can be installed, serviced or adjusted with minimaleffort. When the cam 30 moves in its operating range, the tappet 40 isdisplaced and thereby the braking cable 70 is either tightened tooperate the connected brakes, or released to disengage the brakes. Thecam 30 is positioned in its assembly position for installation of theparking brake system. The braking cable 70 is therefore not tightenedand can easily be assembled or adjusted. For an operation of the parkingbrake system, the cam 30 is turned in its operating range. In a firstposition of the cam 30 in its operating range, the braking cable istightened but does not operate the brakes. A further turning of the cam30 in the operating range results in an increasing displacement of thetappet 40 and thereby in an increasing tension of the braking cable 70,whereby the brake is operated. The cam 30 is turned in its operatingrange, until the tension in the braking cable 70 is sufficient toachieve a desired braking effect.

The tappet 40 is preferably slidably mounted, wherein the displacementaxis is positioned approximately perpendicular to the rotational axis ofthe cam 30. The outer surface of the cam 30 slidingly engages the outersurface of the tappet 40 to move the tappet 40 along the displacementaxis. The tappet 40 is also preferably made of a resistant material, forexample steel, and is provided with a sliding face, positioned parallelto the sliding face of the cam 30. A pressure force from the cam 30 tothe tappet 40 is transmitted via the sliding faces. The pressure forceis transmitted through the tappet 40 to the braking cable 70. The sideof the tappet 40 opposite the cam (i.e., the rounded side as shown inthe Figures) is preferably provided with a cable guiding groove, inwhich the braking cable 70 is guided. The cable guiding groove is shapedto complement the profile of the braking cable 70 and is rounded tominimize friction between the braking cable 70 and tappet 40. The shapeand contour of the guiding surface prevents the tightened braking cable70 from slipping from the tappet 40 when subjected to vibrations.

As best shown in FIG. 2, two guide rolls 50 and 60 are provided whichdirect the braking cable 70 into and out of the operating mechanism 1.During assembly, the braking cable 70 must be pulled into the operatingmechanism 1 for operating the brakes. The guide rolls 50 and 60 directthe braking cable away from a normally linear path to accommodate thetappet 40, and the tappet 40 is positioned to tighten the braking cable70. The guide rolls 50 and 60 are preferably rotatably mounted to avoidfriction at the braking cable 70. They are made also of a resistantmaterial, as they are subjected to similar high forces as the tappet 40and the cam 30. The rotatable axes of the guide rolls 50 and 60 areoriented so that they are on the one hand substantially perpendicular tothe motion direction of the tappet 40 and on the other handsubstantially perpendicular to the motion of the braking cable 70. Eachguide roll 50 and 60 preferably comprises a circumferential cableguiding groove adapted to receive the braking cable 70, thereby tosafely guide the braking cable 70 in the operating mechanism.

The tappet 40 may further include a tappet guide roll 45 rotatablymounted to an end of the tappet 40 opposite the cam. The tappet guideroll 45 preferably guides the braking cable 70 in a cable guiding groovethat is adapted to receive the braking cable 70. By a displacement ofthe tappet 40, the braking cable 70 is displaced via the tappet guideroll 45 and thereby tightened. The friction between the braking cable 70and the tappet 40 is minimized by the rotatable mounting of the tappetguide roll 45. The force compensation between the brakes connected toboth braking cable halves 72 and 74 via the braking cable assemblies isfacilitated, since the braking cable can be displaced with lowerfriction in the operating mechanism.

In the exemplary embodiment illustrated in FIG. 3, the tappet 40 isconnected to two displaceable cable holders 92 and 94 via a flexibleconnecting element 110. A displacement of the tappet 40 causes adisplacement of the cable holders 92 and 94. The flexible connectingelement 110 extends between both cable holders 92 and 94 and transmitstensile forces therebetween. The flexible connecting element 110 engagesthe cam opposing side of the tappet 40 and is movable in response todeviation of the tappet 40. The connecting element 110 may slide alongthe tappet 40 to compensate forces that act respectively to the cableholders 92 and 94.

The flexible connecting element 110 preferably is made arcuate or bandshaped, and produced from a tear-resistant plastic material, compositematerial or a metal. In this embodiment the braking cable includes twobraking cable halves 72 and 74, which transmit the braking force via onebraking cable assembly to the connected brakes. Both cable holders 92and 94 are slidably mounted within cable holder beds 102 and 104 alignedwith the direction of the path of the braking cable halves 72 and 74.The cable holders 92 and 94 connect the braking cable halves 72 and 74with the connecting element 110. The braking cable halves 72 and 74 arepreferably connected to the cable holders 92 and 94 via casted nipplesand appropriate notches (not shown). The connecting element 110 isdeviated by outward displacement of the tappet 40, which pulls the cableholders 92 and 94 toward one another, thereby to tighten the brakingcable halves 72 and 74. To release the braking cable halves 72 and 74,the cable holders 92 and 94 are moved away from each other. To achieveforce compensation between both brakes, the connecting element 110 canslide on the tappet 40, whereby the connected brakes are uniformlyoperated.

In this embodiment, the braking cable halves 72 and 74 areadvantageously moved only in the direction of the cable path. Thebraking cable halves 72 and 74 are not bent, thereby increasing thelifetime of the braking cable halves 72 and 74. Instead, only theconnecting element 110 experiences a bending load. The connectingelement 110, however, may be particularly adapted for bending andsimultaneously transmitting a tensile force, based on its preferred bandform according to the disclosure.

As with the previous embodiment, the tappet 40 may include a tappetguide roll 45 for engaging and guiding the connecting element 110 overthe tappet 40, thereby to further reduce friction between the tappet 40and the connecting element 110. The tappet guide roll 45 is rotatablymounted within the tappet 40 and has a circumference shaped to receivethe connecting element 110. Thereby, a safe guidance of the connectingelement 110 is guarantied, to prevent the connecting element 110 fromslipping from the guide roll 45 of the tappet induced by vibrations.

As shown in FIG. 1, the operating mechanism 1 may be enclosed by ahousing 80, which is shown in an open position. The housing 80 maysupport the components of the operating mechanism 1 and for assembling acompleted operating mechanism 1 to the vehicle. In addition, it protectsthe elements of the operating mechanism 1 from environmental influences,since the operating mechanism 1 is preferably mounted near to the tiresto be braked, and since the mounting position can possibly be at anunprotected position on the outside of the vehicle.

To guaranty a safe operation of the parking brake system, the cabletension within the braking cable 70 or the braking cable halves 72 and74 is measured by means of a force measuring device in a furtherembodiment according to the disclosure. The tensile load may be measureddirectly from the braking cables 70, 72, 74. To this end, the brakingcables 70, 72, 74 respectively comprise two cable halves, which areconnected by means of a slidably mounted force measuring device.Alternatively, the force measuring device is integrated into the tappet40. Therefore the tappet 40 consists of two parts, which are connectedvia a force measuring device. The one part of the tappet 40 is operatedby the cam 30, wherein the other part of the tappet 40 displaces thebraking cable 70 or the connecting element 110. Thereby the pressureforce is measured, that is transmitted by the tappet 40. As a furtheralternative, the force measuring device is connected to one or bothguide rolls 50 and 60 and measures the force, which acts on the guiderolls 50 and 60.

The force measuring device is connected electrically with the controllerof the parking brake system, to control the braking force. The measuringof the force can be done by an arbitrary physical principle. This can bereached for example by resistance strain gauges, the displacement of aspring, or piezo electric gauges.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

1-12. (canceled)
 13. An operating mechanism for at least one parkingbrake having a braking cable, the operating mechanism comprising: amotor unit for driving the operating mechanism; and an eccentricassembly adapted to transform a rotational motion of the motor unit intoa linear motion, the eccentric assembly positioned to engage the brakingcable of the at least one parking brake; wherein movement of theeccentric assembly tightens and releases the braking cable, thereby tooperate the at least one parking brake.
 14. An operating mechanismaccording to claim 13, wherein the eccentric assembly comprises a camcoupled to the motor unit; and a tappet displaceable by the cam, whereinthe tappet is positioned to engage the braking cable.
 15. An operatingmechanism according to claim 14, wherein the tappet is arranged betweentwo guide rolls and wherein the at least one braking cable passes overthe guide rolls and the tappet.
 16. An operating mechanism according toclaim 15, wherein a tappet guide roll is rotatably coupled to the tappetat a cable guiding side, thereby to guide the braking cable and toreduce friction between tappet and braking cable.
 17. An operatingmechanism according to claim 13, in which the braking cable is providedin first and second cable halves, and the tappet is coupled to a firstand a second cable holder, wherein the first and second cable holdersare displaceable along first and second paths aligned with the first andsecond cable halves, respectively, so that a displacement of the tappetcauses a displacement of the first and the second cable holder.
 18. Anoperating mechanism according to claim 17, in which a connecting elementengages the tappet and is connected at opposite ends to the first andsecond cable holders.
 19. An operating mechanism according to claim 18,wherein the tappet further includes a tappet guide roll adapted toengage the connecting element, thereby to guide the connecting elementand decrease friction between tappet and the connecting element.
 20. Anoperating mechanism according to claim 17, wherein the first cableholder is coupled to the first cable half and the second cable holder iscoupled to the second cable half.
 21. An operating mechanism accordingto claim 14, wherein the cam is shaped to have an assembly portion, inwhich the cam causes minimal displacement of the tappet, and a workingrange portion, in which the at least one braking cable is tightened andreleased.
 22. An operating mechanism according to claim 14, furthercomprising a force measuring device adapted to determine the brakingforce generated by the operating mechanism.
 23. An operating mechanismaccording to claim 22, further comprising a controller for the motorunit adapted to receive and interpret signals generated by the forcemeasuring device.
 24. An operating mechanism according to claim 13,wherein the motor unit comprises a motor and a gearbox connectedthereto.
 25. An operating mechanism according to claim 24, wherein themotor comprises an electric motor.
 26. An operating mechanism accordingto claim 24, wherein the gear box comprises a planetary gear.
 27. Anoperating mechanism according to claim 13, further comprising a housing.